San Francisco startup Slack Inc. has raised $42.75 million in Series C funding at a pre-money valuation around $220 million to help business teams communicate without inbox clutter and without having to toggle between dozens of apps, said co-founder and Chief Executive Stewart Butterfield.

Social+Capital Partnership led the investment, joined by the company’s earlier backers Accel Partners and Andreessen Horowitz. Mamoon Hamid, general partner at Social+Capital, has taken a board seat at Slack.

Founded in 2009, Slack was formerly known as Tiny Speck Inc. The startup created a massively multiplayer online game called Glitch, but shuttered it at the end of 2012 to focus on solving a business problem that it identified within its own ranks–clunky, disjointed communications and workflows that were not conducive to worker productivity and happiness.

The company rebranded and released its early version of the Slack app in February.

With about 25 employees today, Slack makes enterprise collaboration and communication software that aggregates messages and information from some of the most-used business and social media apps in the workplace. It also adds a robust search feature allowing employees to find archived data and correspondence that relates to a current project easily.

The startup has a team of full-time employees who constantly review, test and tie business tools or social apps–like Asana, Dropbox , Google+ Hangouts, MailChimp and Pivotal Tracker–to the Slack system.

While Mr. Butterfield believes that email will always have its users, teams that adopt the Slack app tend to “dramatically reduce” their reliance on email for internal communications, he said.

A range of employers, from startups to large corporations, are already using Slack, including Airbnb, Buzzfeed, Comcast and Walmart .

Accel Partners ‘ Andrew Braccia said what impressed him most about the company was its customers’ “relentless appreciation” of the Slack Web and mobile apps, and the quality and number of paying customers signing up to use Slack within a relatively short period.

One trend driving the rapid adoption of Slack is the “BYOA” (or bring your own app) movement, where employees choose to use apps a la carte that will help them get their work done, Mr. Braccia said. Another is the greater interconnectedness between apps, thanks to most tech firms offering APIs that share some of their apps’ functionality or data with others.

“There is an incredibly large opportunity to transform the enterprise productivity suite,” he said. “Some very large companies have been built around that already.”

Investors expect Slack to use the newly raised funding to hire aggressively, localize and sell its system to companies outside of the U.S., and to potentially acquire smaller businesses that will “contribute to or accelerate” its “progress in certain categories,” the investor said.

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